In conventional fuel injection systems, the fuel injectors may be mechanically or hydraulically actuated. In mechanically actuated systems, the pumping assembly which periodically causes fuel to be injected into the engine cylinders is mechanically coupled or linked to a cam driven by the engine so that the pumping assembly is actuated in synchronism with the rotation of the cam. In hydraulically actuated systems, the pumping assembly is hydraulically driven by pressurized actuating fluid which is selectively communicated to the pumping assembly by an electronically-controlled valve. One example of a hydraulically actuated, electronically controlled fuel injection system is disclosed in U.S. Pat. No. 5,121,730 to Ausman, et al. on Jun. 16, 1992.
Another fuel injection system is disclosed in U.S. Pat. No. 4,392,612 to Deckard, et al. As described in connection with FIG. 1 of that patent, the Deckard, et al. fuel injection system has a mechanically actuated pump plunger which acts to periodically increase the pressure in a passage disposed in a spray tip provided with a reciprocable needle valve. When the fuel pressure in the passage increases to a threshold amount, the fuel pressure in the passage forces the needle-valve to open, and fuel is ejected from the spray tip.
The supply of fuel to the spray tip passage and the buildup of fuel pressure in the spray tip passage is controlled by a solenoid actuated, pressure-balanced valve in the form of a hollow poppet valve. When the poppet valve is open, fuel may be supplied to the spray tip passage, and when the poppet valve is closed, the fuel in the spray tip passage may be pressurized sufficiently by the pump plunger to effect injection.
The use of a poppet valve such as the one described in Deckard, et al. may be undesirable when used at very high fuel pressures, such as those in excess of 140,000 MPa (20,000 pounds per square inch or psi), due to fluid leakage at the valve seat when the valve is in the closed position as a result of pressure variations around the periphery of the valve, as described below in connection with FIGS. 1-4.
Referring to FIG. 1, a cross-sectional elevational view of a simple valve 10 is shown. The valve 10 has a valve element 12 that is reciprocable within a valve body 14 between a closed position in which the valve element 12 abuts a valve seat 16 and an open position in which the valve element 12 is spaced from the valve seat 16. The reciprocation of the valve element 12 is controlled by an actuator (not shown). When the valve element 12 is in the open position, fluid is allowed to pass from a bore 18 in fluid communication with the valve inlet, to an annular cavity 20 surrounding a portion of the periphery of the valve element 12, and to a bore 22 in fluid communication with the valve outlet.
Problems may occur with the operation of the valve 10 of FIG. 1 if it were to be used where the fluid in the bore 18 is at a very high pressure, such as in excess of 140,000 MPa (20,000 psi). In particular, such a high pressure in the bore 18 would result in pressure variations within the annular fluid cavity 20 about the periphery of the valve element 12 in a horizontal plane close to the valve seat 16. A rough approximation of such pressure variations is shown in FIG. 2, in which areas of relatively high pressure are represented with the letter "H" and areas of relatively low pressure are represented by the letter "L." Such pressure variations may undesirably result in fluid leakage through the fluid seal at the valve seat 16 when the valve element 12 is in its closed position. Such undesirable pressure variations are present in the cavity 20 even where multiple bores 18 are provided in the valve 10, as illustrated in FIGS. 3 and 4.